Caspi et al (2003)

• Study of theory

  Diathesis-stress theory: if an individual has a specific genetic predisposition toward a disorder (genotype), then interaction with stressors in the environment may cause these genes to be expressed.
• Participants


  847 New Zealand, 26-year olds (members of cohort assessed for mental health on alternative year basis until 21).
• Group 1

  Short alleles
• Group 2

  One short and one long allele
• Group 3

  Two long alleles
• 5-HTT genes


  It is a mutation that has short alleles. Roughly 43% of people have shorter alleles.
• Procedure


  Asked to complete a 'Stressful Life Events' questionnaire which asked them about the frequency of 14 different events between ages of 21-26. Also assessed for depression.
• Results


  People who had one or more short alleles demonstrated more symptoms of depression and suicidal ideation in response to stressful life events (effects stronger for those with more stressful life events).
• Trend observed


  Inheriting the gene is not enough - you need to interact with a stressful environment.
• Strengths


  Holistic approach.
• Limitations


  Correlation - no cause-effect established, assumptions that serotonin causes depression, information of life events was self-reported and therefore unreliable (salience may have played a part), low reliability as further studies did not show same results.